Practitioners in the field of dentistry have long sought polymerizable compositions which would adhere well to dentin. One of the first attempts at bonding to dentin was recorded by Buonocore et al, utilizing a polymerizable mixture containing glycerophosphate dimethacrylate (I): ##STR1## see M. Buonocore, W. Wileman, and F. Brudevold, J. Dent. Res., 35, 846 (1956), and M. Buonocore and M. Quigley, J. Amer. Dent. Assoc., 57, 807 (1958).
Anbar et al have reported dentin adhesives containing vinyl phosphonic acid (II) or vinylbenzyl phosphonic acid (III): ##STR2## see M. Anbar and E. Farley, J. Dent. Res., 53, 879 (1974) and E. Farley, R. Jones, and M. Anbar, J. Dent. Res., 56, 943 (1977).
Various phosphoric acid and phosphonic acid esters have been described as having good adhesion to dentin in patent applications and patents, see, e.g., U.S. Pat. Nos. 4,182,035, 4,222,780, and 4,235,633, O.L.S. No. 2711234, and Japanese laid-open application Nos. 77-113089, 78-30193, 78-39331, 78-67740, 78-69494, 78-110637, 78-113843, 78-134037, 78-144939, 78-138441, 79-21438, and 79-28339. Also, there has been introduced in Japan a dental liner composition, under the name "Clearfil", utilizing a two-part resin system. The first (catalyst) portion of such resin system contains a polymerizable phosphoric acid of undetermined structure. The second (universal) part of such resin system contains an ethanolic solution of sodium benzene sulfinate and N,N-dihydroxyethyl-p-toluidine (the latter compound will be referred to hereafter as "DHPT"). It has been recommended that the use of this composition be preceeded by acid etching of the exposed dentin (e.g., with ortho-phosphoric acid) prior to application of the liner composition. However, the long term physiological affects of such acid etching are unknown, and the efficacy of acid etching of dentin has been questioned by practitioners, see, e.g., M. G. Buonocore, "The Challenge of Bonding to Dentin", The Acid Etch Technique, L. M. Silverstone and I. L. Dogon, Eds., Proceedings of an International Symposium at St. Moritz, Switzerland, Dec. 16-18, 1974, North Central Publishing Co. (St. Paul, 1975). Also, acid etching is a somewhat difficult procedure to carry out, since the highly corrosive acid is injurious to the soft tissues of the mouth. In addition, commercial products containing ortho-phosphoric acid are, in some jurisdictions, subjected to special transportation requirements which increase the costs of shipping dental supplies (e.g. restoration kits) which contain vials of ortho-phosphoric acid.
A non-phosphorus acid compound which is said to possess bonding capability to dentin is reported in U.S. Pat. No. 4,203,220. The preferred compound in said patent is 2-N'-allylamino-4,6-dichloro-1,3,5-triazine (IV): ##STR3##
Organic esters of monofluorophosphoric acid having the formula (V): ##STR4## wherein R is an unsaturated addition polymerizable group have been described as having good adhesion to hard tooth tissues in U.S. Pat. Nos. 3,882,600 and 3,997,504, although no indication regarding the adhesion to dentin of such esters of monofluorophosphoric acid is given in said patents.
In U.S. Pat. No. 3,629,187 there are described various adducts for use as dental resins, made by combining diglycidyl methacrylate of Bisphenol A (hereafter referred to as "BIS-GMA") and isocyanate or diisocyanate. Phosphorus-containing adducts are not described in said patent.
U.S. Pat. No. 2,674,590 describes various poly-condensation products in which phosphorus atoms are linked to two chain-forming aromatic esterifying groups and to one branched aromatic esterifying group containing a diphenyl group. U.S. Pat. No. 2,871,263 describes various phosphoric dihalides in which phosphorus is bonded to two halogen atoms, is doubly bonded to an oxygen atom, and is singly bonded to a monovalent aromatic hydrocarbon radical containing at least one olefinic double bond and having at least one halogen atom attached to a carbon atom therein. U.S. Pat. No. 4,030,933 describes phosphorus and halogen containing polymers prepared by reacting a halogenated derivative of bis(hydroxyethyl)terephthalate with a halogen-containing phosphorus monomer, the resulting polymer having repeating units in which halogen is not bonded directly to phosphorus.
A dentin adhesive composition should desirably offer good adhesion to both dentin and tooth enamel, as well as adhering well to other restorative and composite resins, crowns, and/or orthodontic brackets currently in use ("restorative" and "composite" will be used essentially interchangeably herein, in recognition of the fact that due to differing standards currently in effect throughout the world, an individual dental adhesive composition might be regarded as a "restorative" in some jurisdictions and as a "composite" in others). Also, a dentin adhesive composition should desirably reduce the need for detailed cavity preparation such as undercutting. In addition, a dentin adhesive composition should withstand repeated thermally-induced expansion and contraction while minimizing marginal leakage between the adhesive composition and adjacent tooth tissue or restorative or composite materials. Also, it would be desirable if a dentin adhesive composition offered sufficiently strong bonding to dentin and enamel that the acid etching technique currently used for most dental restorations could be eliminated.